mike mentzer (yah, he was a little crazy) talked about recuperative rates varying as much as sun tolerance and IQ's. some people burn in 5 minutes of sun while others can stay unprotected in sun for hours. there are morons with IQ' under 50, (no offense guys) as well as geniuses with near 200 IQ's.
it makes sense that some people can train hours a day, while others may overtrain on 2 workouts a week (mike called these people recuperative morons)
then again, mike did drink his own piss!!